A controller configured to be coupled to an electric motor. The controller including a processor programmed to receive a signal indicating a stopping command of the electric motor, and control a current such that a capacitor coupled to the electric motor is not overcharged by regenerative energy when a stopping of the electric motor has commenced, wherein controlling the current includes one of the following: upon receiving the signal indicating the stopping command of the electric motor, ramping the current down below a threshold level, or upon receiving the signal indicating the stopping command of the electric motor, forcing the current to circulate in motor windings to prevent regeneration of energy in the capacitor.
Legal claims defining the scope of protection. Each claim is shown in both the original legal language and a plain English translation.
1. A controller configured to coupled to an electric motor, the controller comprising: a rectifier configured to convert an alternating current (AC) input voltage received from a power source to a direct current (DC) link voltage; a DC link capacitor coupled to an output of the rectifier and having a capacitance below 10 μF, the DC link capacitor configured to receive the DC link voltage, wherein the DC link voltage drops to a value of approximately zero during each cycle when the AC input voltage transits a value of zero; an inverter coupled to an output of the DC link capacitor and comprising a plurality of switches configured to condition the DC link voltage to output an AC voltage for driving the electric motor; and a processor coupled to the DC link capacitor and the inverter, said processor programmed to: receive a measurement of the DC link voltage from a voltage sensor coupled to the DC link capacitor; issue a stopping command to stop the electric motor by opening the inverter switches each time the DC link voltage drops to the value of approximately zero; and control current provided to the electric motor to prevent overcharging of the DC link capacitor beyond a maximum voltage rating of the DC link capacitor by regenerative energy when a stopping of the electric motor commences as the DC link voltage drops to the value of approximately zero, wherein controlling the current comprises one of the following: when the DC link voltage has the value of approximately zero, ramping the current provided to the electric motor down below a threshold level before opening the inverter switches, the threshold level being a level at which an amplitude of the current measured by a current sensor on the electric motor must be below before the electric motor is turned off to prevent regenerated voltage from exceeding the maximum voltage rating of the DC link capacitor; or causing a short-circuit condition in windings of the electric motor to force the current to circulate in the windings to prevent any regeneration of energy back to the DC link capacitor when the DC link voltage has the value of approximately zero.
A motor controller manages energy during motor stops to prevent capacitor overcharge. It converts AC power to DC using a rectifier. A small DC link capacitor (less than 10 μF) is used, where the voltage drops to near zero each AC cycle. An inverter uses switches to drive the motor with AC voltage from the capacitor. A processor monitors the capacitor voltage and issues a stop command by opening the inverter switches when the voltage is near zero. To prevent capacitor overcharge from energy regenerated by the motor, the controller either reduces motor current below a safe threshold before opening the switches (the threshold being a current level below which the capacitor won't overcharge) or creates a short circuit in the motor windings, forcing current to circulate and dissipate within the motor itself when the DC voltage is near zero, thus preventing energy from returning to the capacitor.
2. A controller in accordance with claim 1 , wherein ramping the current down below a threshold level comprises: receiving the amplitude of the current; determining the threshold level; comparing the amplitude of the current with a maximum level of current based on the determined threshold level; and ramping the current down below the determined threshold level.
The motor controller, as described in the previous description, reduces motor current before stopping. It receives a current reading, determines a safe current threshold (a current level below which the capacitor won't overcharge), compares the current reading to the threshold, and then reduces the motor current below this determined safe threshold before opening the inverter switches. This ensures that the energy regenerated during the motor's stopping phase doesn't overcharge the DC link capacitor.
3. A controller in accordance with claim 1 , wherein the processor is further programmed to send a signal requesting an inverter to be in an off-state upon receiving the signal indicating the stopping of the electric motor.
The motor controller, as described in the first description, which prevents capacitor overcharge during motor stops, also sends a signal to the inverter to switch off. This happens when the controller receives a command to stop the electric motor. The signal instructs the inverter to enter an off-state, contributing to the controlled shutdown of the motor and prevention of regenerative overcharge.
4. A controller in accordance with claim 3 , wherein the processor is further programmed to, prior to sending the signal to the inverter, ramping the current down below the threshold level.
The motor controller, as described in the previous description, which sends a signal to turn off the inverter when stopping, first reduces the motor current below a safe threshold before sending that turn-off signal to the inverter. This current reduction occurs before the inverter is commanded to switch off, preventing voltage spikes and overcharging of the DC link capacitor due to energy regeneration during the motor's deceleration.
5. A system comprising: an electric motor; and a motor drive circuit comprising: a rectifier configured to convert an alternating current (AC) input voltage received from a power source to a direct current (DC) link voltage; a DC link capacitor coupled to an output of the rectifier and having a capacitance below 10 μF, the DC link capacitor configured to receive the DC link voltage, wherein the DC link voltage drops to a value of approximately zero during each cycle when the AC input voltage transits a value of zero; an inverter coupled to an output of the DC link capacitor and comprising a plurality of switches configured to condition the DC link voltage to output an AC voltage for driving the electric motor; and a controller coupled to the electric motor, the DC link capacitor, and the inverter, the controller comprising a processor programmed to: receive a measurement of the DC link voltage from a voltage sensor coupled to the DC link capacitor; issue a stopping command to stop the electric motor by opening the inverter switches each time the DC link voltage drops to the value of approximately zero; and control current provided to the electric motor to prevent overcharging of the DC link capacitor beyond a maximum voltage rating of the C link capacitor by regenerative energy when stopping of the electric motor commences as the DC link voltage drops to the value of approximately zero, wherein controlling the current comprises one of the following: when the DC link voltage has the value of approximately zero, ramping the current provided to the electric motor down below a threshold level before opening the inverter switches, the threshold level being a level at which an amplitude of the current measured by a current sensor on the electric motor must be below before the electric motor is turned off to prevent regenerated voltage from exceeding the maximum voltage rating of the DC link capacitor; or causing a short-circuit condition in windings of the electric motor to force the current to circulate in the windings to prevent any regeneration of energy in the DC link capacitor when the DC link voltage has the value of approximately zero.
A motor system comprises an electric motor and a motor drive circuit. The drive circuit includes a rectifier to convert AC power to DC, a small DC link capacitor (less than 10 μF) where the voltage drops to near zero each AC cycle, and an inverter with switches to drive the motor using AC voltage from the capacitor. A controller monitors the capacitor voltage and stops the motor by opening the inverter switches when the voltage is near zero. To prevent capacitor overcharge from regenerated energy, the controller either reduces motor current below a safe threshold before opening the switches (the threshold is a current level below which the capacitor won't overcharge) or it creates a short circuit in the motor windings, forcing the current to circulate and dissipate within the motor itself when the DC voltage is near zero.
6. A system in accordance with claim 5 , wherein ramping the current down below a threshold level comprises: receiving the amplitude of the current; determining the threshold level; comparing the amplitude of the current with a maximum level of current based on the determined threshold level; and ramping the current down below the determined threshold level.
The motor system, as described previously, reduces motor current before stopping. It receives a current reading, determines a safe current threshold (a current level below which the capacitor won't overcharge), compares the current reading to the threshold, and reduces the motor current below this determined safe threshold before opening the inverter switches. This ensures the energy regenerated during the motor's stopping phase doesn't overcharge the DC link capacitor.
7. A system in accordance with claim 5 , wherein the processor is further programmed to send a signal requesting the inverter to be in an off-state upon receiving the signal indicating the stopping of the electric motor.
The motor system described earlier, which includes a controller to prevent capacitor overcharge during motor stops, also involves the processor sending a signal to the inverter requesting it to switch off. This signal is sent upon receiving a command to stop the electric motor, ensuring a controlled shutdown and preventing regenerative overcharge.
8. A system in accordance with claim 7 , wherein the processor is further programmed to, prior to sending the signal to the inverter, ramping the current down below the threshold level.
The motor system, previously described, which sends a turn-off signal to the inverter when stopping, first reduces the motor current below a safe threshold before sending the turn-off signal to the inverter. This current reduction occurs before the inverter is commanded to switch off, preventing voltage spikes and overcharging of the DC link capacitor from the motor's regenerative energy.
9. A system in accordance with claim 5 , further comprising a voltage clamping device coupled the capacitor, the voltage clamping device configured to protect the capacitor from being overcharged by regenerative energy, the voltage clamping device configured to absorb the regenerative energy if the regenerated voltage reaches a maximum threshold.
The motor system as described above, which uses a controller to stop capacitor overcharge, further includes a voltage clamping device connected to the capacitor. This clamping device protects the capacitor from overcharge due to regenerative energy by absorbing the energy if the regenerated voltage reaches a maximum threshold.
10. A system in accordance with claim 9 , wherein the voltage clamping device is at least one of a metal oxide varistor, a transient voltage suppressor, and a gas discharge tube.
The motor system, as described in the previous description, which uses a voltage clamping device, utilizes at least one of the following devices for clamping: a metal oxide varistor (MOV), a transient voltage suppressor (TVS), or a gas discharge tube (GDT). These components are designed to protect the capacitor from overvoltage caused by regenerative energy during motor deceleration.
11. A method for controlling a current to prevent overcharging of a direct current (DC) link capacitor coupled to an electric motor by regenerative energy when a stopping of the electric motor has commenced by opening switches of an inverter coupled to the electric motor, wherein the capacitor has a capacitance below 10 μF/kW, the method comprising: converting, by a rectifier coupled to the DC link capacitor, an alternating current (AC) input voltage received from a power source to a DC link voltage, wherein the DC link voltage drops to a value of approximately zero during each cycle when the AC input voltage transits a value of zero; receiving, by a controller coupled to the DC link capacitor, the inverter, and the electric motor, a measurement of the DC link voltage from a voltage sensor coupled to the DC link capacitor; issuing a stopping command to stop the electric motor by opening the inverter switches each time the DC link voltage drops to the value of approximately zero; and upon issuing the stopping command, controlling current provided to the electric motor to prevent overcharging of the DC link capacitor beyond a maximum voltage rating of the DC link capacitor by regenerative energy when a stopping of the electric motor commences as the DC link voltage drops to the value of approximately zero, wherein controlling the current comprises executing one of the following: when the DC link voltage has the value of approximately zero, ramping, by the controller, the current provided to the electric motor down below a threshold level before opening the inverter switches, the threshold level being a level at which an amplitude of the current measured by a current sensor on the electric motor must be below before the electric motor is turned off to prevent regenerated voltage from exceeding the maximum voltage rating of the DC link capacitor; or causing a short-circuit condition in windings of the electric motor to force the current to circulate in the windings to prevent regeneration of any energy back to the DC link capacitor when the DC link voltage has the value of approximately zero.
A method to prevent capacitor overcharge during electric motor stops uses a small capacitor (less than 10 μF/kW). A rectifier converts AC to DC, causing the DC link voltage to drop near zero each AC cycle. A controller monitors the DC link voltage. When the motor needs to stop, the controller opens inverter switches when the voltage is near zero. To prevent overcharging the capacitor with regenerative energy, the controller either reduces the motor current below a safe threshold before opening the switches (threshold is a current level below which the capacitor won't overcharge) or creates a short circuit in the motor windings, forcing current to circulate and dissipate within the motor when the DC voltage is near zero.
12. A method in accordance with claim 11 , wherein ramping the current down below a threshold level comprises: receiving the amplitude of the current; determining the threshold level; comparing the amplitude of the current with a maximum level of current based on the determined threshold level; and ramping the current down below the determined threshold level.
The method for preventing capacitor overcharge during motor stops, as described in the previous description, involves reducing motor current below a threshold. This process includes receiving the current reading, determining a safe current threshold (a current level below which the capacitor won't overcharge), comparing the received current to the threshold, and then reducing the motor current below this determined threshold before opening the inverter switches.
13. A method in accordance with claim 11 , further comprising requesting an inverter to be in an off-state upon receiving the request to stop the electric motor.
The method for preventing capacitor overcharge, as previously described, also includes sending a signal to the inverter requesting it to enter an off-state when a request to stop the electric motor is received. This ensures a controlled shutdown sequence.
14. A method in accordance with claim 13 , further comprising, prior to requesting the inverter to be in an off-state, ramping the current down below the threshold level.
The method for preventing capacitor overcharge, which includes requesting the inverter to turn off, further involves reducing the motor current below the threshold level before sending the request to the inverter to switch off. This ensures safe operation and prevents voltage spikes.
15. A method in accordance with claim 11 , wherein forcing the current to circulate in motor windings to prevent regeneration of energy in the capacitor is performed until the electric motor has stopped or until the current decays below a threshold.
In the method of forcing current to circulate to prevent capacitor overcharge, the current continues circulating in the motor windings either until the electric motor has completely stopped or until the circulating current decays below a certain predefined threshold value. This ensures that the regenerative energy is effectively dissipated.
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March 15, 2013
August 15, 2017
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